package org.apache.lucene.search;

import org.apache.lucene.index.FieldInvertState;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/** Expert: Default scoring implementation. */
public class DefaultSimilarity extends Similarity {

    /** Implemented as
     *  <code>state.getBoost()*lengthNorm(numTerms)</code>, where
     *  <code>numTerms</code> is {@link FieldInvertState#getLength()} if {@link
     *  #setDiscountOverlaps} is false, else it's {@link
     *  FieldInvertState#getLength()} - {@link
     *  FieldInvertState#getNumOverlap()}.
     *
     *  @lucene.experimental */
    @Override
    public float computeNorm(String field, FieldInvertState state) {
        final int numTerms;
        if (discountOverlaps)
            numTerms = state.getLength() - state.getNumOverlap();
        else
            numTerms = state.getLength();
        return state.getBoost() * ((float) (1.0 / Math.sqrt(numTerms)));
    }

    /** Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. */
    @Override
    public float queryNorm(float sumOfSquaredWeights) {
        return (float) (1.0 / Math.sqrt(sumOfSquaredWeights));
    }

    /** Implemented as <code>sqrt(freq)</code>. */
    @Override
    public float tf(float freq) {
        return (float) Math.sqrt(freq);
    }

    /** Implemented as <code>1 / (distance + 1)</code>. */
    @Override
    public float sloppyFreq(int distance) {
        return 1.0f / (distance + 1);
    }

    /** Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. */
    @Override
    public float idf(int docFreq, int numDocs) {
        return (float) (Math.log(numDocs / (double) (docFreq + 1)) + 1.0);
    }

    /** Implemented as <code>overlap / maxOverlap</code>. */
    @Override
    public float coord(int overlap, int maxOverlap) {
        return overlap / (float) maxOverlap;
    }

    // Default true
    protected boolean discountOverlaps = true;

    /** Determines whether overlap tokens (Tokens with
     *  0 position increment) are ignored when computing
     *  norm.  By default this is true, meaning overlap
     *  tokens do not count when computing norms.
     *
     *  @lucene.experimental
     *
     *  @see #computeNorm
     */
    public void setDiscountOverlaps(boolean v) {
        discountOverlaps = v;
    }

    /** @see #setDiscountOverlaps */
    public boolean getDiscountOverlaps() {
        return discountOverlaps;
    }
}
